Phase tracking has an important role in the data recovery process of high-speed serial data receivers because it determines the right one among several over-sampled data. Various techniques for picking the sample have been proposed including tracking the edge movement of input stream and scoring samples based on how close they are to the center of the edges (that is, the center of the eye). However, these prior techniques have problems with fast and large jitter. One problem is that the loop latency existing in the path from the scoring logic to the actual change of picking position based on the score limits the speed at which the system can respond to jitter.
A second problem is that scoring of each picking position based on the edge information assumes each eye has the same number of oversampled data (OSD) (for example, 5 OSDs) and a group (or chunk) of OSDs (for example, 50 OSDs) have consistent information on the jitter. However, these assumptions may not be correct when the jitter is fast and/or large. In response to such jitter, some eyes are 6 OSDs wide, while other eyes may be 4 OSDs wide, or even more or less. In addition, an early OSD and a late OSD may involve different information on jitter in the channel.
Digital Video Interface (DVI) is a standard used in providing video signals between chips and is partially compatible for use with High Definition Multi-media Interface (HDMI) compatible products. DVI includes a specification on the eye characteristics that transmitters and receivers have to meet for interoperability. However, some of transmitters in the market do not follow the DVI specification and are DVI non-compliant transmitters. In such a case, phase trackers that expect signals from DVI compliant transmitter from time to time show poor results (e.g., a noisy screen) with signals from DVI non-compliant transmitters. In addition, some users want to use a spread-spectrum clock to reduce the electromagnetic interference (EMI) in such a way that the input stream becomes DVI non-compliant.
The DVI compliant input and DVI non-compliant input may have a difference in eye shape. Sometimes, DVI compliant signals are said to be “non-coherent” in that in the transmitter, the clock signal does not pass through a phase locked loop (PLL) that is used to create the data signals to be transmitted. Some DVI non-compliant transmitters have the clock signal pass through a PLL that is used to create the data signals to be transmitted. This is sometimes said to be “coherent” and adds an extra delay that sometimes leads to some closed eyes.